1. Field
Example embodiments relate to an electronic circuit, for example, to a receiver for reducing intersymbol interference (ISI) of a data transmission channel and compensating for signal gain loss, and method thereof.
2. Description of the Related Art
As the operating speed of semiconductor chips increases, so too may data transfer rates. A data input/output rate may also increase due to restrictions on the number of pins in the semiconductor chip. ISI may cause the degradation of signal quality in nonlinear components of a data transmission channel.
FIG. 1 illustrates a circuit of an example conventional data transmission channel. Referring to FIG. 1, a signal A output from a transmitter 110 may be transmitted to a receiver 130 through a channel 120. The receiver 130 may include a comparator 132 which may compare a signal B, having passed through the channel 120, to a reference voltage Vref, and an amplifier 134 which may amplify the output signals of the comparator 132.
FIGS. 2A, 2B and 2C illustrate example waveforms of signals transmitted through the data transmission channel of FIG. 1. FIG. 2A illustrates an example signal A output from the transmitter 110 of FIG. 1. FIG. 2B illustrates an example signal B passed through the channel 120 of FIG. 1. FIG. 2C illustrates an example output signal CO of the amplifier 134 of FIG. 1. The output signal CO of the amplifier 134 may have an ‘eye’ characteristic as illustrated in FIG. 3. Referring to FIG. 3, two eyes may exist in the signal CO and jitter noise may be widely distributed between the two eyes. This jitter noise may be caused by ISI.
Jitter noise caused by ISI of a data transmission channel may be removed using a signal shaper circuit, as disclosed in U.S. Pat. No. 5,565,812. Referring to FIG. 4, the signal shaper circuit may include a high pass filter 221, which may include a switched capacitor to receive an input signal IN, a comparator 222, a capacitance 223 and a Schmitt trigger 224. The high pass filter 221 may include two similarly constructed gain stages A and B, with a nominal gain of about 10 and a time constant of about 50 sample periods. The second gain stage B may be followed by the comparator 222. The gain stages may have a balanced, fully-differential structure. This example architecture may improve power supply rejection and immunity to parasitic effects. Amplifiers may be designed in such a way that their common mode operating point may be stabilized. The comparator 222 may have a differential input provided by the gain stages A and B and a single-ended output, and may provide a first approximation of the incoming digital signal. The capacitance 223 may be added at the output of the comparator 222 in order to limit its high-frequency response. The Schmitt trigger 224 may restore signal logic levels. The combination of the comparator 222 and the Schmitt trigger 224 may reduce very fast noise spikes, which may otherwise be sampled and misinterpreted.
The signal shaper circuit illustrated in FIG. 4 may have the frequency response characteristics illustrated in FIG. 5. Referring to FIG. 5, to receive an input signal IN modulated at a specific frequency, noise of frequency bands other than the modulation frequency may be removed. Noise from lower frequency bands may be removed by controlling a cut-off frequency using the switched capacitor, and noise from higher frequency bands may be removed using the Schmitt trigger 224. That is, the signal shaper circuit illustrated in FIG. 4 may improve the signal-to-noise ratio (SNR) of a signal.
However, the characteristics of a data transmission channel may vary with frequency. The gain of a receiver, for example, the signal shaper circuit illustrated in FIG. 4, may vary with channel characteristics as illustrated in FIG. 6, and gain loss may depend on frequency. Accordingly, a receiver capable of reducing ISI of a data transmission channel and gain loss according to frequency may help mitigate several detrimental effects.